<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>

<script>
    let a = 10;    //number
    let b = "10";  //string
    let c = true;  //boolean
    let d = null;  //object    js原始的一个错误
    let e = 100n;  //bigint

    let f ;        //undefined 未赋值的变量

    document.write(typeof(a) + "<br/>")
    document.write(typeof(b) + "<br/>")
    document.write(typeof(c) + "<br/>")
    document.write(typeof(d) + "<br/>")
    document.write(typeof(e) + "<br/>")
    document.write(typeof(f) + "<br/>")
</script>
</html>